Process for the production of photographic gelatino silver halide emulsions



United States Patent US. C]. 96-94 19 Claims ABSTRACT OF THE DISCLOSURE A process for the production of photographic silver halide emulsions by flocculating gelatin and a silver halide which comprises using a flocculating agent a copolymer of sodium, potassium, or ammonium p-vinylbenzene sulfonate and 1-vinyl-2-methyl imidazole, acryol morpholine, ethoxymethyl acrylamide or morpholino-methyl acrylamide.

The present invention relates to a process for the production of photographic gelatino silver halide emulsions. More particularly, the invention relates to a process for the production of photographic gelatino silver halide emulsions by removing salts and water from the emulsions using as a flocculating agent, a copolymer made by copolymerizing p-vinylbenzene sulfonate with another vinyl compound.

A photographic gelatino silver halide emulsion is usually prepared by (1) forming and growing the fine crystals of silver halide by the double decomposition of silver salts and halides in the presence of gelatin, (2) removing excess halide and soluble salt formed by the double decomposition to adjust the silver ion concentration and hydrogen ion concentration of the system, and (3) ripening the emulsion by adding, if necessary, suitable sensi tizers.

In a conventionally adopted process for the preparation of a photographic emulsion, the removal of the salts in the above step (2) has been conducted by gelling the emulsion by cooling after the formation of the fine crystals of a silver halide, cutting the thus formed gel into fine pieces, and then washing them with Water. However, a large amount of water and a long period of time are necessary for this process. Moreover, the concentrations of the silver salts and the halide solutions are restricted to a high level, especially in the case of an emulsion -with a low ratio of gellatin to silver halide, since the concentration of gelatin must be maintained above a definite level in order to carry out the gelatin successfully. The restriction in the concentrations of the solutions causes considerable difliculty in the preparation of photographic emulsions of good quality.

In order to overcome such difiiculties, various methods have been proposed for preparing photographic silver halide emulsions by fiocculating the gelatin together with the fine crystals of silver halides which are formed in the presence of a comparatively small quantity of gelatin, and then redispersing the fiocculates after washing. Among such flocculation methods, there has been proposed a method of adding an inorganic salt, a method of adding an organic solvent. and a method of adding a gelatin derivative or a synthetic high molecular compound. While the method of adding an inorganic salt has the disadvantage that a large amount of the salt is required for the process, the method of adding an organic solvent also has the disadvantage that recovery of the expensive solvent is dilficult.

3,482,980 Patented Dec. 9, 1969 ICC On the other hand, in the method of adding a gelatin derivative or a synthetic high molecular compound, there is the advantage that the process can be caried out successfully with a comparatively low cost. When a synthetic high molecular compound is used for this purpose, usually the gelatin-high polymer complex containing silver halide microcrystals is fiocculated from the solution by lowering the pH value of the system and/or adding a polyvalent metallic salt, after the addition of the high polymer to the silver halide emulsion containing gelatin. The flocculate is re-dispersed by increasing the pH value after washing with .Water, then subjected to the processes of addition of gelatin, addition of sensitizer, ripening, etc., according to the specific requirement before use.

An object of the present invention is to provide an improved process for preparing a photographic gelatin silver halide emulsion having excellent photographic characteristics in which the flocculation can be effected by the addition of a small quantity of the specific flocculating agent, the re-dis-persion of the fiocculate can be easily conducted, and the viscosity increase of the emulsion obtained by the flocculation method is relatively small.

The above object of this invention can be attained by flocculating gelatin together with the fine crystals of silver halides by using as the flocculating agent for photographic gelatino silver halide emulsions a copolymer made by copolymerization of a sodium, potassium or ammonium salt of p-vinylbenzene sulfonic acid with the vinyl compound represented by the following general formula:

OH2= |3H 2 wherein Z represents one of the following radicals:

(wherein R' is CH OC H or Caron,

The suitable content of the vinylbenzene sulfonate in the copolymer used in this invention is between 30 and 95%, preferably between 60 and in molecular ratio of monomers contained in the copolymer. It is preferable that the intrinsic viscosity of the copolymer measured in a 1 N aqueous sodium nitrate solution at 30 C. is between 0.2 and 3.0.

In the present invention, the sodium salt, the potassium salt and the ammonium salt of the copolymer all give similar results.

The copolymerization of the p-vinylbenzene sulfonate and the above-mentioned hydrophilic vinyl monomer is preferably carried out in an aqueous solution. The copolymerization may be conducted with a high polymerization yield by a thermal polymerization using a peroxide,, such as potassium persulfate and hydrogen peroxide, as an initiator, or an oxidation-reduction polymerization using a potassium peroxide-sodium bisulfite system and the like as the initiating system. Isopropanol or an alkyl mercaptan may be added in order to control the degree of polymerization.

As as example of the preparation of the copolymer used in the process of this invention, the copolymerization with acryloyl morplioline is illustrated.

Into 250 ml. of deionized water is dissolved by heating 70.3 g. of potassium p-vinylbenzene sulfonate. Into the aqueous solution were added 29.7 g. of acryloyl morpholine and '50 g. of isopropanol and deionized water is added to bring the total volume to 500 ml. After further adding 0.1 g. of potassium persulfate, the thermal polymerization is carried out for hours with stirring at 60 70 C. in a nitrogen atmosphere.

When the thus produced viscous solution of a copolymer is poured gradually into large excess of methanol with stirring, the copolymer is precipitated as a white fibrous polymer, which is collected by filtration and dried by a hot blast. The yield for the copolymer is 70 g. (70% and the nitrogen analysis value is 1.62%, from which the content of potassium p-vinyl-benzene sulfonate in the copolymer is calculated to be 76.5 mol percent. The intrinsic viscosity of the copolymer when measured is a l N aqueous sodium nitrate solution at 30 C. is 1.02.

For conducting the flocculation using the copolymer of this invention, the copolymer may be added to the emulsion or gelatin in any step before conducting the flocculation, but it is most preferable to add the copolymer of this invention after forming and growing the fine crystals of a silver halide in a gelatin solution.

In order to conduct the precipitation effectively, it is preferable to reduce the pH value of the system by the addition of an acid. An organic acid, such as acetic acid, citric acid, salicylic acid and the like, and an inorganic acid, such as hydrochloric acid, sulfuric acid and the like can be used for this purpose. The pH for conducting the precipitation is preferably below 6, particularly below 5. The addition of a divalent salt, such as, a cadmium or zinc, is particularly eifective in the case of con ducting the precipitation at a comparatively high pH.

The copolymer of this invention may be added to emulsion as a solid, followed by dissolving, but is suitably added as about a aqueous solution. The suitable amount of the copolymer to be added to the emulsion is about to /2 (by weight), preferably from about to A by weight of the gelatin contained in the emulsion at the time of flocculation. The concentration of the gelatin before flocculation is suitably about 0.5 to 10% by weight, preferably below 2% by weight. The process of the present invention may be applied to any silver halide emulsions, such as, a silver chloride emulsion, silver bromide emulsion, silver bromochloride emulsion, silver bromoiodide emulsion and silver bromo-iodochloride emulsion.

The emulsion to which the process of this application can be applied may be chemically sensitized in accordance with a known method, such as, by compounds containing unstable sulfur, e.g., ammonium thiosulfate or allyl thiourea (cf., for example, P. Glafkides; Chimie Photographique; 2eme Edition Photocinema, Paul Montel, Paris, pp. 297-299 (1957)) or by gold compounds, e.g., a complex salt of mono-valent gold and thiocyanic acid, or by the combination thereof. The emulsion may be also optically sensitized by the addition of cyanine dyes, merocyanine dyes, and the like (cf., Shinichi Kikuchi; Kagaku Shashin Binran (Scientific Photography Handbook); published by Maruzen K. K., Tokyo; pp. -24 (1959)). In particular, cyanine dyes having an acid group in the molecule (of, US. Patent 2,503,776) and the similar merocyanine dyes (of, US. Patent 2,493,758) may be profitably used since their dyeing afiinities for the copolymer of this invention are weak. Further, the emulsion may be stabilized by a stabilizer well known in the art, for example, by a heterocyclic compound, such as, benzotriazol, l-phenyl-S-mercaptotetrazol, 4 hydroxy-6-methyl-1,l,3,3a,7-tetrazaindene, or

to precipitate emulsions by using a 6-thioctic acid; by a mercury compound such as mercumallylic acid (cf. Japanese patent publication No. 22,063/ 64), or by benzene sulfinic acid. Further, in the emulsion to be used in this invention may be incorporated a hardening agent, such as, formaldehyde, mucochrolic acid, chrome alum, or a triazine derivative (cf., Belgian Patent 641,044) or such a hardening agent with a hardening aid, such as, resorcinol, and resorcyl aldehyde. Furthermore, into the emulsion may be incorporated a surface active agent such as saponin, sodium alkyl benzene sulfonate or an addition polymer of an alkyl phenol and sultone for improving the coating facility The emulsion in this invention may be also sensitized by using a polyalkylene oxide derivative such as a condensation product of an alkyl phenol and polyethylene oxide.

The photographic emulsion prepared by the process of this invention may be used for the production of color photographic films or color photographic printing papers by adding color couplers to it.

It is already known to use as a viscosity increasing agent a polymer prepared by polymerizing only p-viny lbenzene sulfonate which is used in the process of this invention to synthesize the copolymer of this invention (cf., Japanese Patent No. 264,470). The known polymer can be also used for fiocculating silver halide crystals in a photographic gelatino silver halide emulsion like the copolymer in the process of this invention.

However, the use of the copolymer in the process of this invention has such advantages that the amount of this polymer necessary for the flocculation may be less than that of the polymer consisting of only the p-vinylbenzene sulfonate, and the re-dispersion of the i iocculate obtained by the use of the copolymer of this invention can be carried out easily and the agglomeration of redispersed silver halide particles is reduced as compared with the case of using the known polymer of only p-vmylbenzene sulfonate. Moreover, the viscosity increase of the emulsion obtained by the process of this invention using the copolymer is less than in the case of using the polymer of only the p-vinylbenzene sulfonate.

Further, it has been proposed in Belgian Patent 612,492 polymer made by sulfonating a copolymer of styrene and an acrylamide derivative. The copolymer of the present invention differs from the polymer described in the Belgian patent in that all the styrene groups present in the copolymer of our invention are substituted with one sulfo group for each styrene group, since the copolymers of the present invention is prepared, as described above, by copolymerizing the mixture of sulfonated styrene and another vinyl monomer. The copolymerization of sulfonated monomer gives a more uniform and less contaminated polymer than sulfonation after copolymerization, since the purification of the monomer is easier than that of the polymer.

Moreover, in the above-mentioned Belgian patent, the preferable content of styrene groups is described as being between 97 and and particularly between 97 and while in the present invention the effective content of the styrene sulfonic acid is between and 30% particularly between 60 and 85%. In short, the copolymer in this invention is a diiferent compound from the polymer in the Belgian patent and has different characteristics from those of the polymer in the Belgian patent.

The invention will be further illustrated but is not intended to be limited by the following examples:

EXAMPLE 1 In the example, a photographic silver bronio-iodide emulsion was prepared as follows by using as the flocculating agent the copolymer (I) of acrylamide and potassium p-vinylbenzene sulfonate of which the intrinsic viscosity measured in a 1 N aqueous sodium nitrate solution at 30 C. was 0.870 and the molecular ratio of the p-vinylbenzene sulfonate was 66%.

Solution 1:

Potassium bromide g 80.5 Potassium iodide g 5 Gelatin g Water ml 700 Temperature, 70 C.

Solution 2:

Silver nitrate g 100 Water to make 1200 ml.

Temperature, 62 C.

Half of solution 2 was added to solution 1 in 1 minute and after allowing to stand for 2 minutes the other half of solution 2 was added in 30 minutes. The temperatures of the solution was then decreased to 40 C. in 10 minutes, 12 ml. of a 5% aqueous solution of copolymer (I) was added to the solution followed by sufiicient stirring and 7 ml. of a 10% methanol solution of salicyclic acid Was added to adjust the pH of the solution to 4.2. When the agitation was stopped, the complex of gelatin and the copolymer was agglomerated together with the silver halide particle to cause rapid flocculation and the emulsion was completely precipated after 8 minutes. By decantation, 1500 ml. of the supernatant liquid was removed and to the remaining emulsion was added 1900 ml. of cold water containing 2.8 ml. of 10% salicylic acid followed by stirring for 2 minutes. After stopping stirring and completely precipitating the emulsion, 1900 ml. of the supernatant liquid was removed by decantation. Into the remaining emulsion was poured 1900 ml. of cold water again containing 2.8 ml. of 10% salicyclic acid and after repeating the procedures of stirring, precipitating and removing supernatant liquid (1900 ml.), 650 ml. of water at 60 C. containing 4 ml. of a 2 N aqueous sodium carbonate solution was added into the system to increase the pH to 6.1 and re-disperse the emulsion. Thereafter, a sulfur-containing sensitizer, a stabilizer and a gold sensitizer were added and the emulsion was ripened for a suitable period of time. The thus prepared photographic emulsion had the same photographic characteristics as those prepared by a conventional method and the sensitizing effect by optical sensitizers was not obstructed.

EXAMPLE 2 A photographic silver bromo-chloride emulsion was prepared as follows using as the flucculating agent for the emulsion a copolymer (II) of acryloyl morpholine and potassium p-vinylbenzene sulfonate of which the intrinsic viscosity measured in a 1 N aquecous solution of sodium nitrate at 30 C. was 0.740 and the molecular ratio of the p-vinylbenzene sulfonate was 64%.

Solution 1:

Potassium bromide g 38 Sodium chloride g 40 Cadmium bromide g 8 Gelatin g Water ml 2000 (Temperature, 60 C.)

Solution 2:

Silver nitrate g 100 Water to make, 1300 ml.

(Temperature, 51 C.)

Solution 2 was added into solution 1 in 1 minute and the mixture was ripened for 5 minutes at that temperature. Thereafter, the temperature of the thus obtained emulsion was reduced to 50 C. in 15 minutes and after adding a 5% aqueous solution of compound II, followed by stirring thoroughly, 7.5 ml. of a 10% aqueous citric acid solution was added to adjust the pH to 4.0. When the agitation was stopped, flocculation occurred immediately and the emulsion was precipitated completely in 10 minutes. By decantation, 2600 ml. of the supernatant liquid was removed and then 2400 ml. of cold Water containing 3.7 ml. of 10 citric acid was added followed by stirring for 3 minutes. After stopping stirring and completely precipitating the emulsion, 2400 ml. of the supernatant liquid was removed by decantation and then 1000 ml. of water cont aining 8 ml. of a 5% aqueous sodium carbonate solution Was added to increase the pH to 5.6 and re-disperse the emulsion. The temperature was increased at the same time to 50 C. and then 150 g. of gelatin was added to the emulsion. Thereafter, a sulfurcontaining sensitizer was added and the system was ripened for a proper period of time. The thus prepared photographic emulsion has the same characteristics as those prepared by a conventional method.

EXAMPLE 3 Various photographic emulsions were prepared as in Example 1 using, however, the following copolymers as the precipitating agent for emulsion:

III N -vinylpyrrolidone 95 1. 360 22 IV Acrylolyl morpholine 35 0. 550 35 do 54 0. 620 15 do 77 1. 380 10 VIII do 78 1. 200 12 X do 87 1. 420 12 do 93 1. 080 13 Morphollnomethyl acrylamide 55 O. 600 25 XII. l-vinyl-Z-methyl imidazol. 89 0. 840 35 XIIL Ethoxymethyl acrylamide 71 0. 354 18 XIV Acrylamide 71 1. 800 15 (A) Copolymer number.

(13) Monomer to be polymerized with potassium p-vinylbenzene sulfonate.

(0) Molecular ratio (percent) of potassium p-vinylbenzene sulfonate.

(D) Intrinsic viscosity in 1 N N aN 0 solution at 30 C.

(E) Added amount of copolymer (as 5% solution).

The emulsions prepared by using copolymers III and XIV had almost the same photographic characteristics as those of the photographic emulsion prepared in Example 1.

From the above table, it will be understood that the added amount of the copolymer may be comparatively small in the case Where the molecular ratio of potassium p-vinylbenzene sulfonate is from 60 to The less the amount of the added copolymer, the easier is the redispersion of the flocculate and the lower is the increase in the viscosity of the emulsion obtained.

EXAMPLE 4 After finishing the formation by precipitation of an ammonia-process high-sensitivity silver bromo-iodide emulsion (Ag 11.5 mol percent) containing gelatin 40 g. to 0.6 mol of the silver halide, 40 ml. of a 10% aqueous solution of the copolymer (the intrinsic viscosity in 1 N aqueous sodium nitrate solution at 30 C. was 1.38) of 77 mol percent of potassium p-vinylbenzene sulfonate and 23 mol percent of acryloyl morpholine was added with stirring. The system was diluted with cold water to 1.5 liters to reduce the concentration of gelatin to 2.7% and at the same time to reduce the temperature of the system to 23 C. Thereafter, 210 ml. of 10% sulfuric acid was added to the system while stirring during about 10 minutes to adjust the pH to 5.0. By stopping stirring, the emulsion was flocculated in the form of a fine precipitation flocculate. 1.3 liters of the supernatant liquid was removed. The flocculate was mixed with 2 liters of ol water containing 0.3 g. of salicylic acid followed by stirring to rinse the flocculate. Then, after allowing the system to stand, about 2 liters of the supernatant liquid was removed by decantation. This process was repeated three times. Then, 350 ml. of warm water containing about 0.4 g. of sodium carbonate was added with stirring and the flocculate was re-dispersed at a pH of 7.0 to give about 760 ml. of the concentrated emulsion. The pAg of the emulsion was 8.4 and the electric conductivity thereof was 1100 ohm/cm.

By adding to the emulsion a sulfur-containing sensitizer and a gold-containing sensitizer and subjecting to proper ripening, an emulsion for medical direct X-ray films having good photographic characteristics was obtained.

EXAMPLE The procedure of Example 1 was repeated using the copolymer (the intrinsic viscosity in 1 N NaNO solution at 30 C. was 0.87) of 66 mole percent of potassium p-vinylbenzene sulfonate and 34 mol percent of acrylamide instead of the copolymer in Example 4.

Precipitation, rinsing, and re-dispersion were etfectively carried out in this case also and the pAg and the electric conductivity of the thus obtained emulsion were 8.3 and 1000 aohm/cm, respectively. By applying proper chemical ripening, an emulsion having the same photographic characteristics as in Example 1 was obtained.

What we claim is: n

1. A process for the production of a photographic silver halide emulsion by flocculating gelatin together with silver halide which comprises using as the flocculating agent a copolymer made by copolymerizing (1) a compound selected from the group consisting of sod1um p-vinylbenzene sulfonate, potassium p-vinylbenzene sulfonate and ammonium p-vinylbenzene sulionate with (2) a compound selected from the group consisting of l-vinyl- Z-methyl imidazole, acryloyl morpholine, ethoxymethyl acrylamide, and morpholino-methyl acrylamide.

2. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the molecular ratio of the p-vinylbenzene sulfonate in said copolymer is between 30 and 95%.

3. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the molecular ratio of the p-vinylbenzene sulfonate in said copolymer is between 60 and 85%.

4. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the intrinsic viscosity of said copolymer measured in a 1 N aqueous sodium nitrate solution at 30 C. is between 0.2 and 3.0.

5. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein said copolymer is prepared by the copolymerization of the p-vinylbenzene sulfonate compound with the vinyl compound in an aqueous phase.

6. The process for the production of a photographic silver halide emulsion as claimed in claim 5 wherein said copolymerization is conducted by thermal polymerization.

7. The process for the production of a photographic silver halide emulsion as claimed in claim 5 wherein said copolymerization is conducted by oxidation-reduction polymerization.

8. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein said copolymer is added to the emulsion after the formation of fine crystals of a silver halide in the emulsion.

9. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the flocculation of the emulsion is conducted at a pH below 6.

10. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the flocculation of the emulsion is conducted at a pH below 5.

11. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein said copolymer is added to the emulsion as an aqueous solution.

12. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the amount of said copolymer is between about ,4 and /2 part by weight per 1 part by weight of gelatin contained in the emulsion.

13. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the amount of said copolymer is between about V and /4 part by weight per 1 part by weight of gelatin contained in the emulsion.

14. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the concentraion of gelatin in the emulsion before conducting the flocculation is maintained between about 0.5% and about 10% by weight.

15. The process for the production of a photographic silver halide emulsion as claimed in claim it wherein the concentration of gelatin in the emulsion before conducting the flocculation is maintained between about 0.5% and about 2% weight.

16. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the vinyl compound which is copolymerized with p-vinylbenzene suifonate compound is acryloyl morpholine.

17. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the vinyl compound which is copolymerized with the p-vinylbenzene sulfonate compound is morpholinomethyl acrylamide.

18. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the vinyl compound which is copolymerized with the benzene sulfonate compound is l-vinyl-Z-methyl imidazol.

19. The process for the production of a photographic silver halide emulsion as claimed in claim 1 wherein the vinyl compound which is copolymerized with the p-vinylbenzene sulfonate compound is ethoxymethyl acrylamide.

References Cited UNITED STATES PATENTS 2,837,500 6/1958 Andres et al. "260-63 3,022,172 2/1962 Ohba et al. 96--94 3,178,294 4/1965 Kinkel et al. 9694 3,341,333 9/1967 Klinger et al. 9694 FOREIGN PATENTS 957,417 5/1964 Great Britain. 967,624 8/1964 Great Britain.

NORMAN G. TORCHIN, Primary Examiner MARY F. KELLEY, Assistant Examiner US. Cl. X.R. 961l4; 2l079.3 

